Dear Poppler Developers,
I found that the actual implementation of Type 4 or Type 5 interpoalted
shadings in xpdf/libpoppler are extremely slow and do not display all
shadings correctly (parameterized patches with large triangles are often
wrong).
I have written a stable patch for both issues: it is now about 5 times
faster and displays parameterized patches correctly. It is a small
bugfix combined with a tweaked the triangle refinement.
Furthermore, I have a prototype which implements *real* linear
interpolation for these shadings. It is very fast and looks considerably
better than the piecewise constant approximation introduced by triangle
refinements. It works pretty well up to now. I implemented low level
support for these shadings and specialized the SplashOutputDev for
rendering triangle interpolations, i.e. it works for screen display and
for bitmap output. Quality and display speed match the one of acrobat
reader.
I am sure my additions are valueable and propose them for usage in
libpoppler: the bugfix/speed improvement is directly usable and stable
and the lowlevel shader will need some more time. I could also use some
advice to get the integration with transparency, blending and whatever
correctly. I started with the xpdf sources, so I would also appreciate
any hints how you communicate changes between xpdf and libpoppler if you
are interested in my proposal.
Best regards
Christian
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